Ectodermal differentiation

Notch. The notch gene in Drosophila encodes a receptor-like transmembrane protein with EGF-like repeats. Notch is essential for ectoderm differentiation. 

Liem, K. J., Tremmel, G., Roelink, H. and Jessel, T. Dorsal differentiation of neural plate cells induced by BMP-mediated signals from epidermal ectoderm. Cell 82 969-979, 1995. 

According to the accepted definition SC, resulting in only one type of the differentiated cells, are named unipotential (or monopotential), two - bipotential. Those cells which give the beginning to a few types of different specialized cells are named pluripotential or multipotential. Totipotential is the ability of cell to differentiate in all the types of cells and tissues of organism (in any of 350 specialized lines derivative of ectoderm, mesoderm and endoderm). 

In Xenopus, in addition to the role in 5S RNA gene regulation, somatic HI has been shown to be involved in further stages of differentiation. The restriction of myoD expression, a marker for the loss of the ability by ectodermal cells to differentiate into mesoderm, requires the presence of somatic histone HI [144]. Again, the globular domain alone and not the whole HI molecule is required to confer this effect [142]. 

Stem cells are present in the earliest stage of embryonic development the blastocyst. Embryonic stem cells are pluripotent, meaning they are capable of generating any terminally differentiated cell in the human body that is derived from any one of the three embryonic germ layers ectoderm, mesoderm, or endoderm [8]. All the body s organs arise through a series of divisions and differentiations from the original embryonic stem cells that form the blastocyst [3]. 

Cord blood has long been used as a source of MSCs for bone marrow transplantation. The stem cell compartment is more abundant and less mature in cord blood than in bone marrow. Moreover, MSCs in cord blood have a higher proliferative potential because of their extended lifespan and longer telomeres [91-94]. Not only can cord-blood MSCs be harvested without morbidity to the donor, but they also display a robust in vitro capacity for directable or spontaneous differentiation into mesodermal, endodermal, and ectodermal cell fates. Cord-blood MSCs are CD45 and HLA-II and can be expanded without losing their pluripotency. Therefore, cord blood is also undergoing preclinical evaluation as a possible easily accessible source of multipotent cells. 

MesECTODERM In embryos, a cell layer not yet differentiated into mesoderm and ectoderm but destined to give rise to both. 

A well-fed hydra (Fig. 1-13) appears immortal. Its body cells are sloughed off and replaced at a steady rate so that within a month or so its body has been completely renewed 35 The hydra contains only ten cell types. These include two kinds of stem cells that give rise to the ectodermal and endodermal cells of the body wall as well as small interstitial stem cells (Fig. 1-13) that differentiate nerve cells, germ cells, and the nematocytes or stinging cells. Of the 105 cells in a hydra about 3600 are interstitial stem cells. Each day they generate 400 nerve cells and 1800 nematocyte precursor cells as well as 3500 new interstitial cells. 

Saunders, J.W., Gasseling, M.T., Cairns, J.M. (1959). Differentiation of prospective thigh mesoderm grafted beneath the apical ectodermal ridge of the wing in the chick embryo. Dev Biol. 1,281 -301. 

Figure 1.10 Some characteristics of neuroglial cells. A. The neural epithelium derives embry-onally from the ectoderm and differentiates in neuroblasts and neurons and in spongioblasts that will differentiate in astrocytes, oligodendrocytes, and ependymal cells as well as migratory spongioblasts that may give rise to neurons. B. Major functions of neuroglial cells. C. Schematic shape of astrocytes and oligodendrocytes and their respective locations with respect to the neuron. (Courtesy of Dr. S. Oklund.)...

Rinterknecht E. and Matz G. (1983) Oenocyte differentiation correlated with the formation of ectodermal coating in the embryo of a cockroach. Tissue Cell 15, 375-390. 

The central nervous system arises from a thickened area of the ectoderm called the neural plate on day 19 in the human embryo. This process is referred to as induction. The neural plate then differentiates into the neural tube (providing the origins for the brain and spinal cord) and the neural crest (forming the basis of the peripheral nervous system). The process by which the neural tube arises from the neural plate is referred to as neurulation. To form the neural tube, the neural plate changes shape and forms a pronounced groove, closing from the cranial end to the caudal end. The neural tube has openings on both ends that close on about day 25 and day 27, respectively. 

The action of thalidomide on the production of limb abnormalities in the chick are similar to those produced by nitrogen mustard (165). Only mesodermal tissues are affected differentiation is arrested and the mesodermal cells regroup beneath the ectodermal cap. The latter no longer induces development of the proximal portion of the limb, but only of its terminal part, which explains the occurrence of phocomelia. 

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